There are various methods known in the art that are used to preserve a perishable material or make the material more convenient for transport. For pharmaceutical, biotechnological or food materials, a typical method is freeze-drying (also known as lyophilization or cryodesiccation). This is a dehydration process, which works by freezing the material and then reducing the surrounding pressure and adding only enough heat to allow the frozen water in the material to sublime directly from the solid phase to gas. The resulting freeze-dried product can then be readily reconstituted in solution for future use.
The advantage of a freeze-dried product, is that it is generally more stable during storage and transport and has a longer shelf-life than the equivalent material in solution. However, there are some problems with freeze-drying, in that damage to the material to be preserved can occur during the freezing and drying processes. These problems are to some extent addressed by the addition of cryoprotectants and lyoprotectants to the material to be freeze-dried. However, what is less well recognised is that some perishable materials, especially peptides that contain at least one free cysteine residue, are subject to degradation and damage even after completion of the freeze-drying process. That is, although freeze-drying has a preservative effect, freeze-dried products comprising peptides that comprise at least one free cysteine residue often have a shorter than desired shelf-life. There is a clear need for means to improve the stability of freeze-dried compositions comprising such peptides.